Subtile dosisabhängige Aufmerksamkeitsstörungen im Bereich der Hintergrundbelastung mit Blei im Blut : Bewertung empirischer Studienergebnisse unter Berücksichtigung neuropsychologischer und biochemischer Wirkungsmechanismen von Blei
التفاصيل البيبلوغرافية
العنوان:
Subtile dosisabhängige Aufmerksamkeitsstörungen im Bereich der Hintergrundbelastung mit Blei im Blut : Bewertung empirischer Studienergebnisse unter Berücksichtigung neuropsychologischer und biochemischer Wirkungsmechanismen von Blei
Various studies of children have shown an inverse correlation between levels of lead in the blood far below the HBM-I-value (100 µg/l) and IQ (intelligence quotient) plus different attention functionalities including working memory. Animal testing has shed light on the modulation of synaptic plasticitiy, neuronal apoptosis, neural degeneration and adult neurogenesis due to lead. There are few references to be found on the effects of lead below the HBM-I-value with respect to neurocognition in adults. It is for this reason that the Institute of Hygiene and Environmental Medicine together with the Clinic for Psychiatry and Psychotherapy of the University Hospital Aachen have, within the framework of a pilot study on patients with environmental connected illnesses (Schulze-Röbbecke et al. 1999), examined the effects of lead on attention span. Under statistical control of diverse covariables it was possible to show a positive correlation between the levels of lead in the blood (mean value 27 ± 16 µg/l) and standard deviation of reaction times of working memory (r = 0,45). This can be interpreted as decreased stability of the working memory processing (Kunert et al. 2004). Amongst others the covariables’ stress, socioeconomic status and environmental stimulation can interact with the effects of lead on neurocognition and can bias the study results. Working memory is considered as one of the fundamental components of attention. In its prefrontal neuronal networks working memory represents the object of attention and offers an interface of perception and behaviour in consideration of long-term memory contents. Dopamine intensifies the persisting activity of stimulus specific bi-stable neurons and represses background activity of neurons which provide weaker stimuli. An insufficient dopaminergic input could result in the destabilization of the working memories neuronal networks. A decrease of D1-receptors in the prefrontal cortex could be demonstrated in rats with levels of lead of 130 µg/l after chronic exposure during youth. The homeostasis of calcium sensitive kinases and phosphatases in the working memory is crucial to the desired rapid decline of information once target oriented behaviour has been accomplished (Dash et al. 2007). Due to the lead-induced disruption of calcium metabolism and the direct lead substitution on Calmodulin and Calcineurin, the rapid decline of information is no longer guaranteed. Should the results be substantiated when the study is broadened, there will be further evidence of lead levels in the blood far below the HBM-I-value interfering subtly with central nervous processes. The entirety of studies has led to the cancellation of HBM-values and to the need of a further reduction of lead exposure. Whether or not genetic factors also have an impact on sensitivity to lead of the working memory is not yet known.
